A transmission-type liquid crystal display (LCD) exhibits a high contrast ratio and good color saturation. However, its power consumption is high due to the need of a back light. At bright ambient, the display is washed out completely. On the other hand, a reflective LCD is using ambient light for reading displayed images. Since it does not require a back light, its power consumption is reduced significantly. However, its contrast ratio is lower and color saturation much inferior to those of the transmission type. At dark ambient, a reflective LCD lost its visibility.
U.S. Pat. Nos. 6,281,952 B1; 6,295,109 B1; 6,330,047 B1 each to Sharp describe conventional transflective light crystal displays, where each pixel is split into R (reflective) and T (transmissive) sub-pixels. The R and T area ratio can vary from 7:3 to 3:7, depending on applications. The transmissive display is used for dark ambient only in order to conserve power.
Two types of transflective LCDs have been developed: single cell gap (see FIG. 1a) and double cell gap (see FIG. 1b). In the single cell gap approach, the cell gap (d) for R and T modes is the same. The cell gap is optimized for R-mode. As a result, the light transmittance for the T mode is lower than approximately 50% because the light only passes the liquid crystal (LC) layer once. In the double cell gap approach, the cell gap is d and 2d for the R and T pixels, respectively. In this approach, both R and T have high light efficiency. However, the T mode has four times slower response time than that of the R mode.
A common problem for the above-mentioned approaches is that R and T pixels have different color saturation. For R pixels, the incident light passes through the color filter twice, but for T pixels light only passes the color filter once. As a result, their color saturation is different.
A search in the United States Patent Office of the subject matter of this invention (hereafter disclosed) developed the following five (5) U.S. patents and two (2) U.S. patent publications:
U.S. Pat. No. 5,280,375 to Tsuda, et al., U.S. Pat. No. 5,303,322 to Winston, et al. and U.S. Pat. No. 5,528,720 Winston, et al. all describe optical backlight systems for collecting light and outputting the light, and methods for fabricating a taped multilayer luminary device;
U.S. Pat. No. 6,044,196 to Winston, et al describes an optical device for operating on light from a source and for selectively outputting light to a viewer without concern for the LC structure;
U.S. Pat. No. 6,118,503 to Oki, et al. teaches the use of a polarized lift guide component to enhance the light efficiency by converting the polarization of the backlight;
U.S. Pat. No. 6,256,447 to Laine, et al describes a backlight apparatus for LCD use without concern for the LCD design;
U.S. Pat. No. 6,335,999 to Winston, et al describes an optical device for operating on light from a source and for selectively outputting or concentrating light to guide the LCD backlight;
Patent Publication 2001/0052948 to Okamoto, et al describes a LCD with the LCD element having a pair of substrates sandwiched about the LC layer of two different thicknesses and in which the thickness of the LC layer is thinner in the reflection section than in the transmission section; and,
Patent Publication 2002/0018279 to Molsen, et al describes a light scattering transflector built on the bottom glass of the liquid crystal display panel with a special shape to direct and scatter the ambient light into the reflective region.
The above described common problem of the R and T pixels having different color saturation is not alleviated by the above documents found in the referenced patent search.
A primary objective of the invention is to provide a single cell gap transflective liquid crystal display (LCD) for enhancing brightness of reflected and transmissive images whereby high quality images are displayed when the ambient light sources are low.
A secondary objective of the invention is to provide a single cell gap transflective LCD that has simpler fabrication over double cell gap transflective LCDs.
A third objective of the invention is to provide a single cell gap transflective LCD having a cost benefit over prior devices since only one retardation film is needed.
A fourth objective of the invention is to provide a single cell gap transflective LCD that is compatible with present fabrication methods and does not involve extra time and costs that would be needed with new fabrication methods.
A fifth objective of the invention is to provide a single cell gap transflective LCD that can be applicable on different liquid crystal modes.
A sixth objective of the invention is to provide a single cell gap transflective LCD having a high area utilization.
A seventh objective of the invention is to provide a single cell gap transflective LCD having same response time in both the R and T regions.
An eighth objective of the invention is to provide a single cell gap transflective LCD having same color saturation effects.
Preferred embodiments of the invention includes both methods and apparatus for providing a single cell gap transflective LCD in which the methods include the steps of: providing a transmission portion and a reflection portion in the transflective LCD; and also providing a reflector of the back light in said transmission portion to said reflective portion whereby the reflected back light and ambient light follow similar paths and thereby improves the brightness of the reflected and transmissive images of the transflective LCD and the apparatus comprises: a transmission portion and a reflective portion in the transflective LCD; and a reflecting structure of several different shapes in the path of back light in the transmission portion to reflect transmitted light to the reflective portion so that the back light and ambient light follow similar paths whereby brightness of the reflected and transmissive images are improved.
Further objects and advantages of this invention will be apparent from the following detailed descriptions of presently preferred embodiments, which are illustrated schematically in the accompanying drawings.